A continuation is planned for investigations of the circulatory responses to asphyxia. Several species of marine mammals, in which asphyxial adaptations are highly developed and in which they can be conveniently examined in experiments of apneic diving, will be studied and compared with terrestrial species in which similar but less profound adjustments can be demonstrated. Effort will be concentrated on two general topics: 1) consequences of circulatory responses to asphyxia in the kidneys and the heart and 2) development of circulatory responses to asphyxia. Physiological adaptations to asphyxia and diving include redistribution of blood flow leading to ischemia of kidney and other organs while maintaining perfusion of brain and heart with blood of steadily decreasing oxygen content and increasing carbon dioxide. Enhanced anaerobic capability plays an important role in some tissues. Isolated seal and dog kidneys will be compared in techniques allowing perfusion with gas-equilibrated blood to permit controlled experiments of renal blood flow, metabolic and clearance studies before and after episodes of ischemia. The seal's cardiac output is reduced and heart rate is markedly slowed during diving, but mean arterial pressure remains unchanged. The myocardium is exposed to severe hypoxemia in a long dive. Specific features of the seal heart which permit it to tolerate the conditions of asphyxia incidental to diving will be studied during experimental dives in which myocardial blood flow and oxygen consumption will be measured. Implanted blood flow meters and sampling catheters will be employed. Other investigations will explore the ischemic tolerance of seal heart and the possibility the anaerobic energy sources are utilized. The development of adaptations to diving will be traced and studied during growth in young seals, in which the protective features of asphyxial defense are known to be rudimentary. Preliminary tests indicate that the procedures to be used show promise of successful application of the proposed studies. BIBLIOGRAPPHIC REFERENCES Simon, L.M., E.D. Robin, R. Elsner, A.L.G.J. Van Kessel and J. Theodore. A biochemical basis for differences in maximal diving time in aquatic mammals. Comp. Biochem. Physiol. 47B:209-215, 1974. Wahrenbrock, E.A., G.F. Maruschak, R. Elsner and D.W. Kenney. Respiration and (Text Truncated - Exceeds Capacity)